1. Technical Field
The present disclosure relates to a multi-needle sewing machine provided with a plurality of needle bars having lower ends to which needles are attached respectively and a needle bar selecting unit which selects one of the needle bars to be switchable to a needle location.
2. Related Art
For example, a multi-needle sewing machine having six needle bars have conventionally been used to form an embroidery pattern comprised of a plurality of partial patterns on a workpiece cloth. In sewing an embroidery pattern by the aforementioned multi-needle sewing machine, thread spools with different colors are set so as to correspond to the needle bars respectively. An embroidery pattern is sewn using needle threads of different colors while the needle bars are selectively switched by the needle bar selecting unit.
In one conventional technique, a sewing system uses a plurality of needle sewing machines in order that a sewing time may be reduced or shortened. More specifically, in the sewing system, a plurality of partial patterns is allotted to the respective multi-needle sewing machines so that sewing times of the respective sewing machines are rendered equal to each other or the differences between the sewing times are reduced. Further more specifically, for example, when an embroidery pattern is to be sewn onto workpiece cloths such as T-shirts by the sewing system so that a plurality of the same T-shirts may be made, a plurality of embroidery frames holding respective workpiece cloths is firstly prepared. The multi-needle sewing machines of the sewing system are set so as to sew only allotted partial patterns respectively. In this case, sewing times of the respective multi-needle sewing machines are set so as to be equal to or have small differences therebetween. Accordingly, after the first multi-needle sewing machine has finished sewing the partial pattern on the workpiece cloth, the embroidery frame is immediately attached to the second multi-needle sewing machine so that the remaining partial pattern is sewn on the workpiece cloth, while the next embroidery frame holding the workpiece cloth is attached to the first multi-needle sewing machine so that the partial pattern is sewn on the workpiece cloth. The above-described operations are repeated thereby to reduce a non-operating time as much as possible. Thus, the aforementioned sewing system can reduce an entire sewing time.
However, repeated sewing of the same partial pattern by the multi-needle sewing machines results in variations in the number of stitches between the needle bars in the above-described sewing system. More specifically, the difference in the cumulative stitch number is rendered larger between the needle bar corresponding to a needle thread of a color occupying a relatively larger area of the embroidery pattern and the needle bar corresponding to another needle thread of a color which is less used. This results in differences in a degree of wear between distal ends of the sewing needles of the respective needle bars. Accordingly, the needle of the former needle bar needs to be replaced by a new one earlier than the needle of the latter needle bar.
The above-described problem also occurs in the case where an embroidery pattern is sewn by a single multi-needle sewing machine. For example, needle bars are assigned with respective identification numbers 1 to 6 in a multi-needle sewing machine with six needle bars. One or more thread spools need to be changed when an embroidery pattern to be sewn by the multi-needle sewing machine comprises partial patterns of seven or more different colors. In this case, since the needle bar with a smaller identification number is given priority in selection, the cumulative number of stitches is increased regarding the needle bar with the smaller identification number out of the six needle bars. As a result, the distal ends of the needles attached to the needle bars are worn more severely than the needles of the other needle bars. Furthermore, each needle bar needs to be lubricated periodically. However, since the needle bars have different cumulative stitch numbers, the lubrication needs to be executed on the basis of the needle bar with the larger or largest cumulative number of stitches as described above. Thus, the conventional multi-needle sewing machines have problems to be overcome in conjunction with a maintenance efficiency, such as the differences in the replacement of the needles and the timing of lubrication.